It is well known in the art that many packaged products including food, beverage, pharmaceutical, ophthalmic, and medical products are produced using microbiologically clean (i.e. sterile) packaging conditions in order to improve safety, shelf life, and quality of the end product. Processes using sterile packaging conditions may be referred to as aseptic packaging, extended shelf life (ESL) packaging, shelf stable packaging and/or ultra clean packaging. The level of sterility (i.e. degree to which packaging surfaces and processing conditions are free of microbes) depends on many conditions including the product being packaged (e.g., pH level of product), varying state and country regulations, and the intended shelf life of the packaged product. Sterile packaging conditions are achieved by sterilizing or disinfecting packaging material, sterilizing or pasteurizing the product to be packaged, filling the package with the product in a sterile environment, and sealing the package in the sterile environment.
Packaging sterilization is typically accomplished with heat or chemical based sterilants. These traditional methods of sterilization have noted disadvantages including, but not limited to:                High heat requires more thermally resistant packaging designs which are typically heavier and more expensive, and less environmentally sustainable        High heat requires higher energy consumption and costs        Chemicals are expensive and difficult and dangerous to maintain onsite        Heat and chemical based sterilization systems are complicated and present difficulties in terms of maintaining sterility        Chemical based sterilants may need to be removed with water, creating added expense and environmental pollution        Chemical based sterilants may leave residual traces on packaging material that could potentially contaminate packaged product.        
It is well known in the art that electron beams are utilized for sterilization (disinfection/decontamination) of packaging materials, such as flexible packaging plastic films, caps and closures, plastic and glass cups and jars, preformed pouches with or without spouts, preformed plastic bags with or without spouts, bottles, cans, and/or paper board containers. A number of noted disadvantages arise in the use of electron beams for sterilization of packaging materials. A first noted disadvantage in such sterilization is that maintaining adequate (sufficient/uniform) electron beam dose may be difficult in modern production environments. Illustratively, when sterilizing the interior of bottles or other packaging materials, an appropriate dose is required to ensure that sterilization occurs. Should the dose received exceed an upper threshold, undesirable effects may occur to the packaging materials. Similarly, should the dose fail to exceed a minimum threshold, incomplete sterilization may occur, thereby resulting in contamination of the packaged product. In an exemplary bottle sterilization environment, if a bottle is moved relative to an electron beam emitter, portions of the interior the bottle may receive excessive dosage whereas other regions may receive doses outside of an acceptable range. It is thus desirous to ensure that the dose along the entire interior region falls within an acceptable range to ensure proper sterilization with no side affects (i.e., maintaining dose uniformity within an acceptable range). Beyond the bottle illustration, the challenge of maintaining dose uniformity exists for all three dimensional products.
A further noted disadvantage of the use of electron beams for sterilization is that they generate x-ray radiation as a byproduct. Electron beams and these byproduct x-rays, as forms of ionizing radiation, are hazardous (i.e., carcinogenous), can cause tissue damage and as such there exist government regulations and manufacturing best practices that limit the amount of radiation workers can be exposed to during a typical operation and/or maintenance. As such, it is necessary to utilize appropriate shielding for electron beam processes and associated apparatus in a production environment to prevent undesired human exposure to ionizing radiation. Shielding is typically achieved by utilizing some thickness of a material that is incapable of being penetrated by electron beam or x-ray radiation, e.g., lead, and utilizing an appropriate material handling scheme that enables continual or intermittent transport of material into, through, and out of the electron beam process area while keeping ionizing radiation entering the operating area below a threshold. The shielding material used may be coated with one or more additional layers of differing materials to improve resilience, and/or maintain sanitary operating conditions, and/or to protect the electron beam blocking material. The material handling system may incorporate a range of configurations and structures including, labyrinth paths, change in elevation, shutter doors, baffles to improve the shielding efficiency and reduce the overall size and expense of shielding systems.
Certain prior art shielding systems utilize fully shielded rooms in which the sterilization process occurs. In such environments, human operators do not enter the production space during sterilization operations. A noted disadvantage of creating shielded rooms is that the size of a production room may be significant, thereby requiring substantial costs in procuring materials to create the shielded room.
Certain techniques have been developed to reduce the size and material required to produce effective shielding for production environments that utilize web based materials. For example, U.S. Pat. No. 4,252,413, entitled METHOD OF AND APPARATUS FOR SHIELDING INERT-ZONE ELECTRON IRRADIATION OF MOVING WEB MATERIALS, the contents of which are hereby incorporated by reference, describes one technique for shielding in a web based material environment. However, a noted disadvantage of such systems is that they are not suitable for use in non-web based environments, e.g. for sterilization of liquid packaging containers, such as bottles or cups.
Exemplary techniques for sterilization are taught in U.S. Pat. No. 6,407,492, entitled ELECTRON BEAM ACCELERATOR, U.S. Pat. No. 6,833,551, entitled ELECTRON BEAM IRRADIATION APPARATUS and U.S. Pat. No. 7,759,661, entitled ELECTRON BEAM EMITTER, the contents of such patents and patent application are hereby incorporated by reference. However, these techniques include a number of noted disadvantages. For example, they fail to provide support to correct the intermittent interruption of electron beams by, e.g., arcs, nor do they provide the ability to continue operations when a single emitter fails. Further, they fail to control dose uniformity for irregularly shaped geometries.